#191F34

CSS

:root {
  --sombre-night: #191f34;
  --sombre-night-rgb: 25 31 52;
  --sombre-night-oklch: oklch(0.244 0.041 271);
}

.element {
  color: var(--sombre-night);
  background-color: hsl(227 35% 15%);
  border-color: oklch(0.244 0.041 271);
}

Tailwind CSS v4

@theme {
  --color-sombre-night: #191f34;
  --color-sombre-night-50: #f1f5ff;
  --color-sombre-night-100: #e3e7f6;
  --color-sombre-night-200: #ced4e6;
  --color-sombre-night-300: #b0b6cd;
  --color-sombre-night-400: #959eb8;
  --color-sombre-night-500: #7c85a2;
  --color-sombre-night-600: #697189;
  --color-sombre-night-700: #545a6e;
  --color-sombre-night-800: #3c4251;
  --color-sombre-night-900: #292e38;
  --color-sombre-night-950: #171a23;
}

SCSS

$sombre-night: #191f34;
$sombre-night-rgb: 25, 31, 52;
$sombre-night-light: mix(#fff, $sombre-night, 20%);
$sombre-night-dark: mix(#000, $sombre-night, 20%);

.element {
  color: $sombre-night;
  box-shadow: 0 0 0 2px rgba($sombre-night, 0.35);
}